Was any Doctor of the Church martyred?
No, after reading up on all the doctors of the church, it looks like of all the Doctors of the Church declared thus far, the only ones who were even on the cusp of martyrdom were:
- St. Augustine of Hippo, who died of illness during battle raging outside the city walls (not sure if he would have been specifically martyred though)
- St. Athanasius, who probably would have been a martyr if he had just stayed dead when exiled numerous times.
- St. Ephrem, who might have otherwise been martyred under Julian the Apostate had he not been exiled
- St. Leo the Great, who by the grace of God was spared from Attila the Hun by his shrewdness and saved a good chunk of Christendom.